Machine parts, particularly rotating parts of turbine engines such as the blades, which may be impacted by foreign bodies, gradually deteriorate as the machine is used. This is the case in particular of the areas reinforced by applying a layer of stellite (a very hard material), which deteriorate owing to the high levels of friction to which they are exposed.
In order to comply with the safety standards, the parts and more specifically the stellite areas, must have a maximum level of wear, without the risk of needing to be replaced. Hence, during the maintenance phases, the parts are examined in order to ascertain whether their level of wear is acceptable or unacceptable. In the event of unacceptable wear, the part must be replaced.
A known method for inspecting the level of wear of the turbine engine parts involves an operator:                disassembling the parts;        measuring the thickness of the parts using contact three dimensional measuring machines;        comparing these measurements with tolerance ranges and        determining whether these parts can be reinstalled on the turbine engine or whether they need to be replaced.        
This method does not allow precise measurement of the thickness of the parts. Indeed, several parameters negatively influence measurement of the parts.
Firstly, the operations, performed by the operator, are repetitive. Thus and this particularly applies to measurement and comparison of the measurements, the operator's visual acuity gradually decreases over a working day and the operator may, at the end of the day, interpret a measurement incorrectly. This may for example be the case for the last part of a series of identical parts.
Secondly, contact tridimensional measurement machines use components such as scale readers or probes that may become out of adjustment or worn over time. In this case, these components require recurrent calibration or replacement. These calibrations need temporary immobilisation of the machine and incur a high operating cost.
Thirdly, the probes commonly used comprise a rod with a ball at the end that contacts the part to be measured. Although quite precise measurements can be obtained, some areas of the part, particularly areas that are difficult to access or very small, may not be reached by the sensor. Thus, the part cannot be measured in the best possible manner.
Finally, mounting the part on a bench of the measurement machine and the wear of said bench affect the quality and result of the measurement. Thus, repeatability of the measurement is not optimal.